25/09/2012. Capgras Syndrome. Chapter 2. Capgras Syndrome - 2. The Neural Basis of Cognition

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1 Chapter 2 The Neural Basis of Cognition Capgras Syndrome Alzheimer s patients & others delusion that significant others are robots or impersonators - paranoia Two brain systems for facial recognition - cognitive feature analysis, matching to stored info - emotional feeling of familiarity, positive affect In Capgras, 1 st system okay, damage to 2 nd system Capgras Syndrome - 2 Neuroimaging shows damage to right temporal lobe (amygdala & connecting circuits) Amygdala is emotional evaluator Feelings of familiarity + positive affect Emotional decision making Emotional memories 1

2 Capgras Syndrome - 3 Damage to right prefrontal area schizophrenics have diminished activity in frontal lobes when hallucinating area involved in distinguishing real and imagined events (or plausible vs. implausible events) Schizophrenics can t distinguish hallucinations from reality Alzheimer s patient generates weird hypotheses about unfamiliar person How the Brain Works Note importance of many areas of the brain working together in recognizing a person Visual processing (occipital lobe) Matching visual input to stored faces Recognizing who the person is (family, friend, neighbour etc.) Recalling person s name (phonological retrieval) Feeling of familiarity Emotional response (like or dislike the person) If person looks different, generate hypothesis why (new glasses or haircut, or space alien) Sinkman Article What explanations have been proposed for Capgras Syndrome? What symptoms did the three patients have in common? What symptoms exhibited by Sinkman s patients are inconsistent with the explanation of Capgras Syndrome offered by Reisberg? What explanation does Sinkman offer? 2

3 The Principle Structures of the Brain 1. Brain Stem - Includes hindbrain, midbrain & diencephalon (thalamus and hypothalamus) 2. Hindbrain - Key life functions heart rate, respiration rate, posture & balance - includes medulla oblongata (continuous with spinal cord), pons (above medulla) & cerebellum - Cerebellum involved in coordination of movement & balance, motor learning - Reticular System- Regulates brain s level of alertness in pons and medulla The Principle Structures of the Brain 3. Midbrain (Mesencephalon) - above pons, below diencephalon - coordinates eye movements - relays auditory information to forebrain - regulates experience of pain The Principle Structures of the Brain 4. Forebrain - diencephalon & telencephalon (or cerebrum) - outer surface is cortex - hills (convolutions or gyri) & valleys (sulci) - longitudinal fissure separates 2 hemispheres - 4 lobes: frontal, parietal, occipital & temporal - central (or Sylvian) fissure separates frontal & parietal lobes 3

4 The Principle Structures of the Brain 5. Subcortical structures - diencephalon: thalamus & hypothalamus - thalamus: relay station for sensory information going to cortex - hypothalamus: control of eating, drinking, sex - limbic system: - hippocampus - memory & learning - amygdala emotional evaluator - commissures bundles of fibres that connect the two hemispheres of the brain - corpus callosum largest body of fibres connecting the two hemispheres 4

5 Neuroimaging Techniques - CAT scans (computerized axial tomography) X-rays - PET scans (positron emission tomography) measures blood flow in the brain - MRI (magnetic resonance imagery) changes in magnetic field - fmri (functional MRI) scans brains of awake people in real time. Measures blood flow and oxygen use. - ** Any cognitive task requires use of many brain areas. Localization of function is not 100% specific Neuroimaging Tong et al. Study Evidence for functional specialization - Activation in fusiform face area (FFA) when Ss shown faces - Activation in parahippocampal place area (PPA) when Ss shown houses, landscapes, - Binocular rivalry different stimuli to each eye S sees only one stimulus at a time. Perceptions alternate - fmri scans show activation patterns reflect Ss conscious perception The Primary Motor Projection Areas Contralateral control: left side of brain controls right side of body - Ipsilateral = same side - Contralateral = opposite side - In front of central fissure in frontal lobe (See Figure 2.1 in text) - Areas of brain control movement in specific areas of body (See Figure 2.2 in text) - Stimulation produces specific movements 5

6 The Primary Sensory Projection Areas 1) Somatosensory behind central fissure in parietal lobe 2) Visual in occipital lobe 3) Auditory upper part of temporal lobe adjacent to Sylvian fissure or lateral fissure - Each area provides a map: (1) map of body, (2) map of visual space, (3) map of frequencies 6

7 The Primary Sensory Projection Areas 1) Somatosensory map body parts represented according to sensitivity to touch, not actual size 2) Visual left visual field processed in right hemisphere, right visual field in left hemisphere - each eye represented in both hemispheres 3) Auditory left ear projects to right hemisphere and right ear to left. Contralateral connections 7

8 Association Areas - nonprimary motor areas initiation and coordination of movements - nonprimary sensory areas interpretation of sensory info & cross-modal integration - deficits: - Apraxias initiation of voluntary movement - frontal lobe - Aphasias language disorders - Broca s area expressive disorder - Wernicke s area receptive disorder - Angular and supramarginal gyri dyslexia, discalculia, disconnection syndrome - Neglect usuallyright parietal lobe damage - Agnosias inability to identify stimuli - modality specific - occipital (visual), temporal (auditory) - Frontal lobe damage disorders of planning & strategy implementation, inhibition of responses, Capgras Syndrome 8

9 The Visual System Parts of the Eye Cornea, iris, lens, retina, fovea Photoreceptors: Rods - dim light, no colour vision, in peripheral vision Cones - colour vision, in foveal vision, higher acuity than rods fine detail Optic Nerve - Rods & cones bipolar cells ganglion cells = optic nerve - Optic nerve lateral geniculate nucleus (LGN) in thalamus occipital lobe 9

10 The Visual System Lateral Inhibition Lateral Inhibition Observed at many levels in visual system Retinal cells A, B, & C stimulated by light, adjacent cell D not stimulated. Cells A. B, & C strongly inhibit all adjacent cells. Cell D inhibits Cell C weakly. Cell C inhibited strongly by B & weakly by D. Cell B inhibited strongly by both A & B. More total inhibition for B than C. Cell C more active than Cell B. cells on edge of stimulation are more active than cells in middle of stimulation and less active then cells not being stimulated. Edge enhancement Neurons Parts of a Neuron - Cell Body - Axons send signals to other neurons - Signal is all or nothing. Cell fires or not. - If cell fires, tips of the axon branches release neurotransmitters - Synapse gap between axon and dendrite - Neurotransmitters taken up by dendrite of second neuron - Dendrites receive stimulation from other neurons 10

11 Neurons - 2 Dendrites receive stimulation from other neurons - Neurotransmitter changes in postsynaptic membrane activation of second neuron - Activation level varies in size. If activation reaches threshold, the cell fires. - Signal is all or nothing - Frequency of firing varies depending on input - Input (excitatory & inhibitory) from many connecting neurons determine whether a neuron fires or not. - Single-cell recording record firing rate of individual neurons in response to various stimuli. - Receptive Field size and shape of area in visual world to which cell responds. Receptive Fields Center-surround Cells - increase firing in response to dots of light in specific locations in visual field - Light in center of receptive field has one effect (increasing or decreasing firing) and light is surround has opposite effect - Light over entire receptive field has no effect - found in LGN & projections of LGN in cortex (Area V1) Receptive Fields - 2 Edge & Line Detectors: cells that respond to lines or edges of a particular orientation. - different cells respond to different orientations. Movement Detectors respond when line or edge moves in certain direction Angle Detectors respond to angle of particular size 11

12 Parallel Processing - Different layers in V1 & different areas of visual cortex have different jobs. - Parallel processing Mutual influence between different processes - fast processing - Parvocellular cells in LGN. specialized for spatial analysis & form. - Magnocellular cells in LGN. specialized for motion detection & depth perception Parallel Processing What System: occipital temporal - object identification - damage visual agnosia Where System: occipital parietal - location information, guides action - damage difficulty reaching Colour System can have selective loss of colour perception Akinetopsia loss of movement perception world appears as series of static movements 12

13 Putting the Information Together Binding Problem How integrate information from different brain areas? 1)Spatial position- adjacent cells in visual system usually relate to adjacent spatial positions in visual field. Spatial position is tracked - adjacent cells in brain respond to adjacent areas of visual field Spatial location provides a frame of reference for binding various attributes. Putting the Information Together - 2 2) Neural synchrony - Suppose vertical line moving to left - Line detectors, orientation detectors & motion detectors all fire at certain rates depending on strength of stimulus - If firing is synchronized pattern (line), orientation & movement all ascribed to same object - Synchronized firing observed when animal is attending to specific stimulus Putting the Information Together - 3 3) Attention - Conjunction errors error in binding features occurs when memory is overloaded - Treisman pop out effect - Need attention to perceive combination of features - Red triangle in set of blue triangles easy to see; red triangle in set of blue triangles & red circles difficult to see. 13

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